394 OUTLINES OF CHORDATE DEVELOPMENT 



pr.s 



B 



FIG. 158. A. Surface view of embryonic shield of a dog of thirteen to fifteen 

 days. B. Surface view of embryonic shield of dog showing medullary plate, 

 etc. From Minot (Laboratory Text-Book of Embryology), A, after Bonnet. 

 A.o., Area opaca; A. p., area pellucida; Kn., Hensen's knot or node; Md., 

 medullary plate; md.F., medullary furrow; ps., pr.s., primitive streak; Sh. t 

 embryonic shield. 



